Who is Participating?

We do this all the time at work using a pair of links in an HTML email
the links go to a script on your server that prepares and sends the email back to the user.

process:
1. user1 fills out form includes email address
2. hits send
3. asp page grabs details, posts to database, sends email to specified user
4. generate HTML email including a link that identifies the database entry
say
<a href ="confirmEmail.asp?confirm=y&id=101">confirm reply</a>
<a href ="confirmEmail.asp?confirm=n&id=101">deny reply</a>
5. send email from server
6.approving person recieves email
7. clicks on link of choice, this will open browser window
8. confimEmail.asp does its stuff knowing both if it is confimed and the ID of what was (or was not confirmed) and hence the email address from step one can be retrieved and it sends the relevant reply to that email address.

we use it to manage confimation emails, just make sure you obtusificate (sp?) the ID to prevent users messing with the URL and hence your database. As we use it for room bookings our ID is date-time-ID so a user would have to jag all 3 to mess it up.